1. Field of the Invention
The invention pertains to the synthesis of organic chemicals which are useful pesticides.
2. Description of the Prior Art
Pyrethroid type insecticides and pesticides possess broad spectrum activity, in addition they have as a general rule low mammalian toxicity and are found to be non-persistent in the environment. Thus this class of insecticidal-pesticidal compounds is of great commercial interest and economical, high yield processes affording the pesticides are much sought after and offer considerable advantages from a manufacturing point of view.
Cyclopropane carboxylic acid and certain derivatives thereof are useful and valuable pyrethroids and intermediates for the preparation of pyrethroid type insecticides and pesticides and there are several art procedures which can be utilized to prepare the above referred to substituted cyclopropane carboxylic acid intermediates.
One potentially advantageous method of preparation of substituted cyclopropane carboxylic acids is taught by G. B. Payne, J. Org. Chem., 32, 3351 (1967), wherein ethyl (dimethylsulfuranylidene)acetate (II) is reacted with activated olefinic compounds (e.g. an olefine of formula III) to yield the corresponding cyclopropane carboxylic acid ester (IVa) as hereinbelow graphically illustrated: ##STR1## The ylide utilized in the above reaction can be conveniently prepared by reacting dimethyl sulfide with an equimolar or excess amount of ethyl bromoacetate to obtain the corresponding sulfonium salt (I) as hereinbelow illustrated: ##STR2## WHICH IS THEN CONVERTED TO THE ABOVE YLIDE (II) with a base: ##STR3##
Indeed, W. I. Fanta and J. I. Schulman, U.S. Pat. No. 3,823,177 issued July 9, 1974, utilize Payne's method to prepare ethyl 2,2-dimethyl-4,5-benzospiro[2,4]hepta-4,6-diene-1-carboxylate (IVb) by reacting Payne's ylide (II) with 1-isopropylideneindene in refluxing dry methylene chloride under an argon atmosphere as hereinbelow graphically illustrated: ##STR4##
The reactions demonstrated above are useful laboratory procedures and yield the desired intermediates and products in satisfactory yields. However, because of poor thermal stability of the sulfonium salt (I) which decomposes at moderately low temperatures as illustrated below: ##STR5## and, more particularly, because of the thermal and hydrolytic instability of the ylide (II) as illustrated below: ##STR6## the utility of these (and similar) reagents in the preparation of cyclopropane carboxylic acids in large amounts is impractical. Since the scaling-up of reactions necessarily involves increased reaction times as well as longer separation and charging cycles, utilization of unstable intermediates necessarily means reduced product yields.
Furthermore formula (I) sulfonium salt is strongly hygroscopic, and requires therefore extra precautions in preparing, handling and storing this intermediate to avoid additional losses.